Algoritmos genéticos: uma abordagem paralela baseada em populações cooperativas

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência da Computação.O trabalho desenvolvido consta da proposição, teste e análise de resultados, de uma estrutura de paralelização para algoritmos genéticos. A estrutura proposta está baseada em um conjunto de populações cooperantes que evoluem em paralelo, onde a troca de material genético, entre as populações, se processa através de indivíduos migrantes. A estrutura para implementação baseia-se na tecnologia de orientação a objetos, sendo que a mesma pressupõem a exploração do paralelismo de máquina através das redes de computador, bem como a exploração do paralelismo local - máquinas multiprocessadas - pela utilização de threads. O trabalho descreve os resultados obtidos com um protótipo construído para simular toda a estrutura proposta. Neste, o paralelismo de máquina foi simulado através de programação concorrente, com a utilização de threads. Os resultados obtidos demonstram a viabilidade da proposta e indicam a necessidade de novas pesquisas buscando testar a estrutura em modo real, sobre um ambiente distribuído

Mac Layer And Routing Protocols For Wireless Ad Hoc Networks With Asymmetric Links And Performance Evaluation Studies

In a heterogeneous mobile ad hoc network (MANET), assorted devices with different computation and communication capabilities co-exist. In this thesis, we consider the case when the nodes of a MANET have various degrees of mobility and range, and the communication links are asymmetric. Many routing protocols for ad hoc networks routinely assume that all communication links are symmetric, if node A can hear node B and node B can also hear node A. Most current MAC layer protocols are unable to exploit the asymmetric links present in a network, thus leading to an inefficient overall bandwidth utilization, or, in the worst case, to lack of connectivity. To exploit the asymmetric links, the protocols must deal with the asymmetry of the path from a source node to a destination node which affects either the delivery of the original packets, or the paths taken by acknowledgments, or both. Furthermore, the problem of hidden nodes requires a more careful analysis in the case of asymmetric links. MAC layer and routing protocols for ad hoc networks with asymmetric links require a rigorous performance analysis. Analytical models are usually unable to provide even approximate solutions to questions such as end-to-end delay, packet loss ratio, throughput, etc. Traditional simulation techniques for large-scale wireless networks require vast amounts of storage and computing cycles rarely available on single computing systems. In our search for an effective solution to study the performance of wireless networks we investigate the time-parallel simulation. Time-parallel simulation has received significant attention in the past. The advantages, as well as, the theoretical and practical limitations of time-parallel simulation have been extensively researched for many applications when the complexity of the models involved severely limits the applicability of analytical studies and is unfeasible with traditional simulation techniques. Our goal is to study the behavior of large systems consisting of possibly thousands of nodes over extended periods of time and obtain results efficiently, and time-parallel simulation enables us to achieve this objective. We conclude that MAC layer and routing protocols capable of using asymmetric links are more complex than traditional ones, but can improve the connectivity, and provide better performance. We are confident that approximate results for various performance metrics of wireless networks obtained using time-parallel simulation are sufficiently accurate and able to provide the necessary insight into the inner workings of the protocols